I'm not sure about the best, but one of the worst I remember is Senel X Shirley from Tales of Legendia as it just felt super forced and was one of the very few times I remember being unhappy with a canon pairing. It was basically one sided on Shirley's end as Senel was in love with her older sister Stella, who was believed to be dead at the game's start. Senel views Shirley as a younger sister and even calls her such. Throughout the game Senel X Chloe is hinted at, though to be fair this is also largely one sided on Chloe's end as Senel is pretty oblivious to her feelings. (This was the pairing I wanted if we couldn't have Senel x Stella as they actually had good chemistry together and didn't fringe on creepy sibling territory.) Then you find out Stella is actually alive, except she dies for real shortly after you find out. Senel is obviously devastated, as Stella loved him back. Yet at the very end of the main story we get fed this garbage about how Senel actually loved Shirely all along, even instead of Stella somehow...? It made no sense to me, and I honestly feel like if Chloe just had the courage to confess first things could have easily gone way different. It's made even worse by the character quests after the main game, in which they pretty much admit to them not having any real romantic/dating relationship to speak of. The whole thing just made me so mad, and it didn't help that Shirley was one my least favorite characters to start with (she literally spends the whole main quest getting kidnapped and doing nothing useful, and by the time you finally get her as a playable character in the character quests she's not really necessary as her skills are basically just a blend of Will's and Norma's).